Vertical antenna with inflatable support and transmission line feed



April 23, 1968 1 s. PEARLMAN 3,380,059

VERTICAL ANTENNA WITH INFLATABLE SUPPORT AND TRANSMISSION LINE FEED Filed Feb. 11, 1965 LESTER S. PEARLMAN INVENTOR.

Umm/LM 0. ATTORNEY United States Patent O 3,380,059 VERTICAL ANTENNA WITH INFLATABLE SUP- PORT AND TRANSMISSION LINE FEED Lester S. Pearlman, Bethel, Conn., assigner to General Precision Inc., Little Falls, NJ., a corporation of Delaware Filed Feb. 11, 1965, Ser. No. 431,839 1 Claim. (Cl. 343-829) ABSTRACT F THE DISCLOSURE The present invention relates to transmission lines and particularly to a light-weight transmission line, which has a low attenuation loss at high frequency.

A conventional light-Weight transmission line usually comprises a pair of concentric, coaxial, copper cylinders of diiferent diameter, which are separated by non-conductive annular spacers. One problem with such a conventional transmission line is that it is normally too heavy for use as a feed line for a light-weight, portable, high-frequency, mast-type antenna.

In accordance with one embodiment of the present invention, a transmission line of the same impedance as a conventional transmission line can be made, which is substantially lighter than a conventional line, and which can be used with the aforementioned mast-type antenna, by using an elongate, inflated, plastic cylinder having a pair of metallic strip conductors bonded thereto.

Accordingly, it is one object of the invention to provide a transmission line, wich has a substantially lower unit weight than conventional transmission lines.

It is another object of the invention to provide a transmission line, which has substantially lower attenuation loss and similar losses at high frequency than conventional transmission lines.

It is a further object of the invention to provide a transmission line, which has suicient rigidity to be substantially self-supporting for use as an antenna mast.

In general, the present invention provides a transmission line between a radio transmitter and its antenna, i.e., there is a positive side conductor of the transmission line leading from the transmitter to the antenna and a negative side conductor to complete the circuit. The transmission line is formed from an inflatable non-conductive structure with a longitudinal axis. A multiplicity of elongated conductor strips are peripherally spaced about said axis and integrally connected to the structure. These conductor strips are so connected in parallel that the connected parallel strips forming the conductors are alternately spaced in a peripheral direction about the longitudinal axis. That is to say no two strips of the same conductor forming the positive side of the transmission line are adjacent to each other but on the contrary each strip of the positive conductor is adjacent a strip of the negative conductor.

Other objects of the invention will become apparent upon reading the annexed detailed description in connection with the drawings wherein like parts are designated by like numerals throughout the several views, and wherein:

FIG. 1 is a sectional view of an antenna mast;

FIG. 2 is a sectional view taken on line 2--2 of FIG. 1;

ice

FIG. 3 is a sectional view taken on line 3-3 of FIG. 1;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 1; and

FIG. 5 is a sectional View taken on line 5-5 of FIG. 2.

Referring to the drawings, one embodiment of the present invention is a transmitting line 10 comprising a pair of elongate electrical conductors 14, 16, and an integrally connected inflatable structure 12. Structure 12, which is a non-conductive container, has a deflated, collapsed portion 18 and an inflated column-shaped portion 20. Column 20 is vertically disposed to form a mast.

Structure 12 has a base member 22 for storing deflated portion 18, and has a clamp means 24 for separating inated column 20 from deflated portion 18 and for preventing gas flow therebetween. Base 22, which rests on grade 26, supports clamp 24, which in turn supports column 20 at one end thereof. Clamp 24 is also a common end terminal for conductors 14, 16.

Column 20 has guy means 28 for resisting wind loads and similar forces. Column 20 also supports a radio antenna 30, which is a terminal at one end of conductor 12. Column 20 also has a sleeve 32 for making an interconnection between column 20 and a transmitter (not shown).

Column 20 (FIGS. 1 and 3) has a peripheral wall 34 with a radially outer surface 36 and with a longitudinal axis 38. Column 20 also has a pair of axially-spaced end walls 40, 42, which together with wall 34 form a cavity 44. In one sample of embodiment 10, column 20 is a cylindrical structure with a height-to-diameter ratio of over 100. Walls 34, 40, 42 are composed of a non-porous, flexible material, such as a high-strength plastic, or the like, so that cavity 44 is substantially air-tight for containing a suitable gas, such as helium. Walls 34, 48, 42 have a sufficient thickness 46 to withstand a substantial inner pressure. In one sample of embodiment 1t), thickness 46 was about 0.003 inch. Wall 34 has a plurality of axially-spaced intlation ports 48, 50 for filling cavity 44 with said gas.

One side of the transmission line, eg., the positive side consisting of conductor 14 (FIGS. 1, 3) has a lower end portion 52, which connects to clamp 24 and which is attached to lower end wall 40, an upper end portion 54, which connects to antenna 30 and which is attached to upper end wall 42, and an intermediate portion 56 which has four parallel branches or strips 58, 60, 62, 64 that are attached to wall 34 and that are substantially equi-spaced in a peripheral direction around axis 38.

The other side of the transmission line, e.g., the negative side consisting of conductor 16 (FIGS. 1, 3) has a bottom end portion 66, which also connects to clamp 24 and which is also attached to lower end wall 40, and also has an intermediate portion 68 which has four parallel branches or strips 70, 72, 74, 76 that are `attached to wall 34 and that are substantially equi-spaced in a peripheral direction around axis 38 and that are alternately spaced between respective branches 58, 60, 62, 64. Clamp 24 effectively short-circuits the transmission line.

Strips 78, 72, 74, 76 (FIGS. 2, 5) have respective radial portions 78, 80, 82, 84, which extend in a radially outward direction from wall 34 adjacent to wall 42 and which overlap guy means 28. Radial portions 78, 80, 82, 84 effectively dene the ground plane over which is mounted antenna 30 extending to a height of one-quarter of the wave length.

Strip 58 (FIG. 3), which is preferably identical to the other seven strips and which is described in detail hereafter, is preferably -a fiat metal strip, such as a thin-film copper strip. Strip 58 has a non-conductive corrosioninhibiting coating 85 on its radially outer side. Strip 58 has a radially inner side 86 bonded to outer surface 36 by an adhesive 88. Strip 58 has a rectangular cross-section of thickness 90 and of dimensional width 92. Width 92 remains substantially constant in dimension in an axial direction along column 20. Wall 34 has a spacer section 94 adjacent to strip 58 in order to accurately x the position of strip 58 relative to adjacent strip 70. Section 94 is defined by a dimension or spacing 96. Spacing remains substantially constant in size in an axial direction when wall 34 is inflated. A ratio of width 92 to spacing 96 is preferably constant for all eight strips. With a construction having a constant width-to-spacing ratio, it is easier to provide a standard impedance which is typical for a coaxial transmission line of conventional design. In one sample of embodiment 10, column 20 was about ten inches in diameter and each strip had a width of about two inches and a thickness equal to 0.001 inch with spacing 96 equal to about two inches. With such construction, strip 58 can stillen wall 34 and can resist tension and cornpression forces whereby column 20 is substantially improved in strength and rigidity.

In the aforementioned sample of embodiment 10, which has a constant width-to-spacing ratio, its attenuation loss at a typical frequency of 460 mc. was about one-half of the corresponding attenuation loss of a prior art coaxial cable that had the same impedance rating. A theoretical reason for such reduction in attenuation loss of embodiment is that spacer section 94 has its edges facing its adjacent strips thereby substantially avoiding any interference with the flux pattern flowing between said adjacent strips.

Clamp 24 (FIGS. l, 4) has a ground wire 93, which is connected to a ground rod 100 that is inserted in grade 26 whereby antenna 30 and conductors 14, 16 can act as lightning arrestors. Clamp 24 is adjustable relative to column 20 for raising and lowering antenna 30 by increasing or decreasing the height of column 20.

Guy means 28 includes four guy ropes 102, 104, 106, 108, which are composed of a high-tensile strength material, such as nylon or metal.

Antenna 30 (FIG. 5) includes a post 110, which extends outwardly in an axial direction from, and which is integrally connected to, wall 42, and also a conductive means 112 which is attached t0 post 110 by an adhesive S8, or the like. Post 110 has a wall 114, which is composed of an inflatable material similar to that of column 20. Post 110 encloses an inner space 116 which communicates with cavity 44 so that antenna 30 is inated simultaneously with column 20. Conductive means 112, which is preferably a film or coat of metal similar in construction to strip 58, is connected to conductor 14 at end 54.

Sleeve 32 (FIGS. l, 3), which is a metal ring encircling column 20 coaxially therewith, has a radially inner face 118, which is in contact with coating 85 on each of the strips of conductors 14 in order to provide a capacitive coupling therewith. Sleeve 32 is adjustable in an axial direction relative to column 20 in order to vary its distance 120 from clamp 24. Sleeve 32 also has a transmitter cable 122 lfor connection to a transmitter (not shown). Distance 120 is equal to one-quarter of a Wave length of the frequency of said transmitter (not shown) which feeds sleeve 32. In one sample of embodiment 10, distance 120 is set at about seven inches in length from clamp 24 for use with a transmitter (not shown) of 400 mc. input. As is well known in the art the short circuit portion of the transmission line below sleeve 32 which is `formed by clamp 24 causes no loss of power in the transmission line but serves as a lightning arrestor.

In summary, this invention provides a transmission line 10, which has a substantially lower unit weight and which has a substantially lower line loss and which has a substantially greater strength and rigidity than the prior art transmission line.

While the present invention has been described in a preferred embodiment, it will be obvious to those skilled in the art that various modiiications can be made therein within the scope of the invention. For example, conductors 14, 16 can be spiral-wound around column 20 for minimizing interference; or column 20 can have a shape of a conical frustum instead of a cylinder and its strips can have a gradually tapering width-to-spacing ratio. It is intended that the appended claim cover all such modiications.

What is claimed is:

1. A transmission line comprising:

an inflated non-conductive vertically disposed structure with a longitudinal axis, said structure having a peripheral wall and axially spaced end walls composed of non-porous material and forming a substantially air-tight cavity containing a lighter-than-air gas for providing a weightless structure, said gas having a pressure greater than atmospheric pressure for increasing the strength and rigidity of said transmission line and further serving as a dielectric;

a coaxial, adjustable conductive sleeve on said structure displaceable relative to said structure in an axial direction and having a radially inner surface, said sleeve serving to couple the output of a transmitter to said transmission line and adjusted to one-quarter wave lentgh of the transmitted signal;

a pair of elongated conductors peripherally spaced about said axis and integrally connected to said structure, each of said conductors having a plurality of spaced branches arranged in parallel and alternately spaced in a peripheral direction about said axis, so that each branch of one of said conductors is adjacent a branch of the other conductor, said branches being flat strips of identical width and identical spacing therebetween and having the same width-tospacing ratio in one cross-section as in another crosssection transverse to said axis axially displaced therefrom, said conductors having radially outer surfaces with non-conductive coatings disposed thereon contacting said sleeve inner surface and forming a constant gap so that a capacitive connection is formed between said sleeve and said conductors;

a base support for said structure and guy means for forming said structure into a vertical structural mast;

an adjustable clamp for said structure encircling an intermediate portion thereof and forming and separating an inated column portion from a deated co1- lapsed portion, said clamp being displaceable in an axial direction relative to said structure for adjusting the height of said inflated column portion, said clamp further contacting said conductors forming a common short-circuit terminal therewith and having a ground wire and ground rod so that said conductors can function as lightning arrestors; and,

an antenna post supported by said structure at one end thereof having conductive means forming a circuit with said conductors, said antenna post being a hollow, integral extension of an end portion of said structure, said post being simultaneously inflatable with said structure.

References Cited UNITED STATES PATENTS 1,285,940 11/1918 Chodakowski 343-915 2,853,706 9/1958 Trench et al 343-915 2,907,875 10/ 1959 Sey Fang 343-915 3,273,062 9/ 1966 Raabe 343-706 X ELI LIEBERMAN, Primary Examiner. 

